1. Field of the Invention
The present invention relates to a load balancer, and in particular to a load balancer for relieving concentrations of a server load.
2. Description of the Related Art
Various forms of load balancers have been known. An example thereof is shown in FIG. 16 where a load balancer LB receives a packet transmitted from a client CL through routers R1 and R3, and selects one of servers as a destination to be connected according to a source address (SA) included in an IP header of the packet or to a combination of the source address and a TCP port number.
Also, there is a form of designating a server distribution destination on an upper application level, or a system of selecting a server according to a URL of the destination to be connected for example.
Moreover, server distributions have been made possible by identifying an SSL (Secure Sockets Layer; an encryption protocol for ensuring TCP/IP communication security on a transport layer) session ID or a Cookie variable for identifying a user where a WWW server generates character string information “Cookie variable” to be stored by both of a server and a browser.
Another significant point as to functions of such a load balancer is a function of server consistency (transaction consistency) during communications.
For example, when server loads used for online shopping are balanced, a “consistency maintenance function” is essential for maintaining a correspondence between the client and the server during a series of flows from a product selection to a purchase and a settlement thereof.
In case of a load balancer unprovided with such a consistency maintenance function, accesses are distributed to different servers during the communication, so that a series of processing of an electronic commerce can not be operated properly.
Therefore, many of the load balancers are provided with the consistency maintenance function based on IP header information.
While the client CL shown in FIG. 16 is a fixed terminal, a mobile IP technology for managing movements of terminals on an IP protocol is currently proposed by the IETF (Internet Engineering Task Force). This technology is for maintaining a communication even if an IP terminal moves, and realizes the mobile communication by acquiring a new care-of address (CoA) whenever the IP terminal moves and by registering the care-of address in a home agent (HA) or a destination terminal.
When a server is accessed from an IP terminal utilizing this technology and when a server load balancing is performed, an IP address (care-of address) of the IP terminal is changed whenever it moves, so that the source address is changed. Therefore, the function of server consistency maintenance during communications using the source address (or combined with the source address) cannot be accomplished.
This will be described referring to a schematic diagram of a packet transmission when a mobile IPv6 is utilized as shown in FIG. 1.
A packet whose source address (SA) is a care-of address CoA1 when a mobile node (hereinafter, referred to as mobile IP terminal) MN is connected to a router R1 belonging the area or a care-of address CoA2 when connected to a router R2 belonging the area by the movement is prepared and transmitted.
Assuming that the load balancer LB is provided between the router R3 and servers S1, S2 in the same way as in FIG. 16, when the load balancer LB receives such a packet and uses the source address (SA) as a retrieval (selection) key in the same way as in FIG. 16, the load balancer misidentifies an access from the same mobile IP terminal MN as an access from another mobile IP terminal, thereby changing the server S1 to S2, so that there has been a problem that the server consistency cannot be guaranteed.